"And I heard a loud voice saying in heaven, Now is come

salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night.

"And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death." - Revelation 12:10-11 KJV

They overcame him by the blood of the Lamb: Jesus' death, burial, and resurrection.

And by the word of their testimony: their testimony of their repentance, baptism in Jesus name, and receiving the Holy Ghost.

They overcame him by the Gospel and by their obedience to the Gospel!

"Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil; and deliver them who through fear of death were all their lifetime subject to bondage." - Hebrews 2:14-15 KJV